# Cleidocranial Dysplasia > Cleidocranial dysplasia for NEET-PG Orthopaedics: RUNX2 mutation, hypoplastic or absent clavicles, open fontanelles, supernumerary teeth and short stature. - Canonical URL: https://prepelephant.com/topics/neet-pg/orthopaedics/cleidocranial-dysplasia - Exam / course: NEET-PG · Subject: Orthopaedics - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-15 - Last updated: 2026-10-15 - Reference basis: Maheshwari's Essential Orthopaedics; Apley's System of Orthopaedics and Fractures; Campbell's Operative Orthopaedics - How to cite: "Cleidocranial Dysplasia", PrepElephant, https://prepelephant.com/topics/neet-pg/orthopaedics/cleidocranial-dysplasia ## Direct answer Cleidocranial dysplasia is an autosomal dominant skeletal disorder, most often caused by mutations in the RUNX2 gene, which regulates osteoblast differentiation. Its hallmark is hypoplastic or absent clavicles, which allow the shoulders to be brought together in front of the chest. Delayed closure of the fontanelles and sutures, supernumerary teeth and short stature complete the classic picture. ## What you must remember - **Inheritance:** autosomal dominant, with many cases arising from new mutations; the RUNX2 (CBFA1) gene is the usual culprit. - **Clavicle:** hypoplasia or complete absence, most often bilateral, which permits abnormal approximation of the shoulders. - **Skull:** wide open anterior fontanelle and sutures, frontal bossing and a broad head, with wormian bones on X-ray. - **Teeth:** supernumerary teeth, delayed shedding of primary teeth and delayed eruption of permanent teeth, often with a high arched palate. - **Pelvis:** wide pubic symphysis and delayed pubic ossification, a useful radiographic clue. - **Stature and intellect:** short stature, usually mild, with intelligence that is normal. - **Management:** largely supportive, with dental care and physiotherapy for shoulder function; surgery is reserved for cosmetic or functional problems. ## Building the diagnosis from the clavicle outwards A 10-year-old boy has drooping shoulders that meet in front of his chest and a wide, open anterior fontanelle on examination. The reasoning starts at the clavicle and widens to the skull, teeth and pelvis. 1. **Test the shoulders:** ask the child to bring both shoulders forward until they meet, and palpate for short or absent medial clavicles. This manoeuvre is the feature that most often prompts the diagnosis. 2. **Examine the skull:** feel for an open anterior fontanelle and widely separated sutures, and note frontal bossing. These findings reflect defective intramembranous ossification. 3. **Inspect the teeth:** look for supernumerary teeth and delayed eruption of permanent teeth, which a dental surgeon often notices first. 4. **Image the skeleton:** radiographs show hypoplastic or absent clavicles, wormian bones, a wide pubic symphysis and delayed pubic ossification. 5. **Consider genetic testing:** a RUNX2 mutation is found in many, but not all, typical cases, so testing helps when the clinical features are incomplete. 6. **Plan supportive care:** most children need no clavicle surgery, and physiotherapy, dental care and periodic review of shoulder function form the core of management. ## Viva angles on the clavicle and the skull Examiners usually check whether you can link a clavicular defect to the rest of the syndrome. - **Trap:** treating the absent clavicle as an isolated congenital defect. **Correct:** the clavicle is one part of a syndrome, so check the skull, teeth and pelvis before deciding anything. - **Trap:** attributing open fontanelles to rickets. **Correct:** in cleidocranial dysplasia the fontanelles stay open because intramembranous ossification is defective, and the clavicular and dental features separate it from rickets. - **Trap:** expecting a RUNX2 mutation in every case. **Correct:** the mutation is not identified in every typical case, so the diagnosis rests on clinical and radiological findings. ## Frequently asked questions ### Which gene is mutated in cleidocranial dysplasia? Cleidocranial dysplasia is most often caused by mutations in RUNX2, also called CBFA1, a transcription factor needed for osteoblast differentiation. Loss of normal RUNX2 function disturbs intramembranous ossification, which explains the clavicular, skull and dental features of the condition. ### Why can children with cleidocranial dysplasia bring their shoulders together? The clavicles are hypoplastic or absent, so the scapulae can be drawn medially across the front of the chest. This manoeuvre is the sign examiners most often use to prompt the diagnosis of cleidocranial dysplasia. ### Which dental features point to cleidocranial dysplasia? Supernumerary teeth, delayed shedding of primary teeth and delayed eruption of permanent teeth are the classic dental features of cleidocranial dysplasia. A high arched palate is also common, so dental review is a routine part of the assessment. ### Does cleidocranial dysplasia need surgery for the clavicles? Surgery is not needed for most patients with cleidocranial dysplasia, because the shoulder girdle usually functions well. Operative correction of the clavicles is reserved for cosmetic concerns or significant functional limitation, and the decision is individualised. ### How does cleidocranial dysplasia differ from rickets on examination? Rickets causes bowed limbs, widened growth plates and abnormal biochemistry, whereas cleidocranial dysplasia shows clavicular hypoplasia, open sutures and supernumerary teeth with normal calcium and phosphate. Radiographs of the clavicles and pelvis help separate the two conditions.